Many communication systems operate using a centralised scheduler which is responsible for allocating transmission resources to different nodes so that they are able to communicate with one another.
A typical example is the uplink of the UMTS LTE (Long Term Evolution), where the uplink and transmissions from different secondary stations, also named User Equipments (UEs), are scheduled in time and frequency by the primary station of the cell, also named the evolved Node B (eNB). The primary station transmits a “scheduling grant” message to a secondary station, indicating a particular time-frequency resource for the secondary station's uplink transmission, typically around 3 ms after the transmission of the grant message. The grant message also typically specifies other transmission parameters, e.g. the data rate or power to be used for the secondary station's transmission.
If the secondary station is at the limit of communication range, for instance at the cell edge, the uplink transmission rate is typically limited by the available transmit power of the secondary station. In such a case, it may be desirable to be able to transmit a data packet using a small amount of resource in the frequency domain and an extended resource in the time domain.
This kind of approach is already proposed for instance in 3GPP for LTE, and is known as “TTI bundling”, where TTI is a Transmission Time Interval. Here, the secondary station transmits a packet using a small amount of resource in the frequency domain (e.g. 1 Resource Block), but extending over more than one subframe. The number of subframes in a TTI bundle is currently assumed to be configured semi-statically—i.e. by higher-layer signalling, which may be updated occasionally but not for every packet transmission. In general, the higher layer signalling is slower than normal signalling. TTI bundling is more efficient than sending multiple transmissions over successive subframes, since only one downlink control message is required, and only one ACK/NACK needs to be sent for the whole bundle. The Use of TTI bundling (and the bundle size) is configured semi-statically for instance by higher layer signalling. The TTI bundling approach is intended to be applied in the case of VoIP where very small resource allocations in the frequency domain are appropriate (e.g. 1 RB), and the data packet size does not vary.
However, the problem addressed here is that currently available signalling channels are not efficient for the envisaged application or effective in changing the degree of bundling dynamically which would be desirable to match changing packet sizes and/or changes in the radio channel.